1. Field of the Invention
The present invention relates generally to measuring devices, and more particularly to a measuring device which measures uterine characteristics and automatically responds to conditions indicative of parturition or labor so that appropriate actions may be taken to suppress or manage labor, either by administration of tocolytic agents or other means.
2. Description of the Prior Art
The inability to detect the onset of premature labor or parturition has proved to be a dilemma to both pregnant women and their health care professionals. It is not uncommon for women to unexpectedly give birth before arriving at a medical facility. Additionally, the occurrence of false labor, and the inconveniences related thereto, are commonplace. Thus, there has been an attempt to develop accurate labor detection devices.
Each year in the U.S., 5% of all infants are born prematurely at an enormous cost to the health care system. Premature births account for 85% of neonatal deaths. About 10% of pregnant women in the U.S. are at risk of premature labor. Accurate detection or prediction of the occurrence of premature labor would allow the patient to be appropriately treated to suppress labor, thereby improving the chances that delivery will occur closer to term. The closer the delivery is to term, the lower the mortality rate and the lower the cost post-delivery neonatal care.
Several methods have been employed or proposed for detection or prediction of premature labor. These include both natural and instrument-based means.
Symptomatic self-monitoring is a natural means whereby the mother is educated in the symptoms of uterine contractions or cervical dilatation and receives regular counseling from a nurse. This approach has the advantage that it is non-invasive and inexpensive, since it can be done at home. However, it requires significant discipline, is time consuming for the patient, and lacks uniform accuracy. Mammary stimulation, cervical distensibility, and fetal breathing movements encompass other natural means. However, these methods require that the patient visit a care provider. They are therefore expensive and inconvenient.
Intrauterine pressure (IUP) measurement devices are considered to be the most accurate means available for measuring frequency of occurrence, duration, and intensity of uterine contractions. This technique has frequently been used to validate the accuracy of other methods of monitoring uterine activity. In this method a transvaginal catheter is inserted into the uterus. Open lumen fluid-filled catheters may be used, but require regular flushing to keep the lumen free of cellular debris. Catheters have been constructed with a balloon tip to eliminate the need for regular flushing. Microballoon-tipped catheters provide poor accuracy Larger balloons provide better accuracy but their presence leads to irritation and artifactual stimulation to both uterus and fetus. In addition, their use is restricted to bed-ridden patients and there is a risk infection. Catheters that employ a solid state pressure transducer at the tip or fiber optic technology have also been used. These devices are available from companies such as Hewlett Packard (HP Model 113975A). These devices are useful only in a limited number of circumstances and only for bed-ridden patients, typically following a membrane rupture. Additionally, these devices increase the risk of infection. An implantable pressure telemetry device has also been used (Smyth, 1960) for monitoring intrauterine pressure. This device has been introduced into the uterine cavity external to the membranes to measure IUP following induction of labor. The authors suggest its use to "extending obstetric research and treatment control." No reference is made to using this device as a tool for prediction or detection of premature labor.
With the exception of symptomatic self-monitoring, use of the above methods has been restricted to a care provider's office. However, successful treatment preterm labor depends on early diagnosis (Iam, et. al., 1990) and these methods do not provide the timely information needed to effect prompt intervention and arrest labor. Methods suitable for monitoring patients as they go about their daily activities present a significant advantage in early diagnosis of preterm labor.
The guard-ring tocodynamometer provides a non-invasive means for monitoring uterine activity and represents the current state-of-the-art for detecting premature labor in ambulatory patients. This device is placed on the maternal abdomen and held in place by an elastic belt. It employs a "guard-ring" to flatten the abdomen within an area over which pressure applied to a sensing diaphragm by the abdominal tissues is sensed. Pressure measurements taken at this flattened area are representative of intrauterine pressures. Some commercially available tocodynamometers are capable of transmitting data to a clinic or doctors office via telephone lines. These devices are manufactured by Tokos of Santa Ana, Calif.; Healthdyne of Marietta, Ga.; and Orion. of Ft. Meyers, Fla. All of these devices are ineffective under certain circumstances. Additionally, they are prone to false alerts since a rise in abdominal pressure may be caused by application of external forces such as exercise, a hand pushing on the abdomen, or gastric activity.
Parturition may be determined by utilizing information from physiological changes, such as temperature changes, vulva swelling, cervical dilation, and uterine contractions with varying degrees of success and forewarning.
Several technologies, such as ultrasound and remote sensing, have been utilized in the determination of the onset of parturition. For example, U.S. Pat. No. 3,606,879 (Estes) discloses an ultrasonic apparatus which is used for monitoring uterine contractions and cervical dilations by measuring the change in transit times of each pulse of ultrasonic energy. Additionally, fetal heartbeat may be determined by monitoring the change in frequency, due to a doppler effect, of an ultrasonic wave which passes through a fetus.
In an attempt to detect parturition, temperature sensors have been utilized to detect temperature changes in animals. For example, U.S. Pat. No. 4,651,137 (Zartman) discloses an intravaginal parturition alarm and method for its use. The device comprises an anchor, a temperature sensing means affixed to the anchor, and an alarm means. The anchor has a diameter that is smaller than an interior diameter of a posterior portion of the animal's vagina at the onset of parturition, but greater than the interior diameter prior to the onset parturition. The anchor's diameter is also smaller than an interior diameter of an anterior portion of the female's vagina before and at the onset of parturition such that the anchor is retained in the anterior portion for a period prior to parturition and expulsed at the onset of parturition. The sensing means senses temperature differential at the location of the anchor before and after expulsion and activates an alarm means based upon this temperature change. Additionally, intravaginal pressure may be measured for a period days prior to parturition by inserting the device and taking a measurement. This process is repeated daily to determine a standard intravaginal temperature for the female at a particular time. As is obvious, this method is highly invidious and will not apply with respect to human females.
Aside from the use of the temperature change upon expulsion of an object from the reproductive tract as an indicator of parturition, others have attempted without success to show a reliable relationship between temperature phenomena and the onset of parturition and related events. Research reports may be summarized as describing a body temperature increase during the latter part of pregnancy, with a substantial drop during the last few days to a few hours before parturition. However, for a number of reasons, the efforts of workers in the field to develop a reliable relationship between temperature phenomena and the onset of parturition have failed.
In fact the prior art would actually lead one away from the use of temperature measurements as a reliable tool in the forecasting and identification of occurrences related to parturition. Researchers in the field generally reported failures in their attempts to use such measurements in forecasting and determining occurrences related to parturition, thus dissuading other researchers from further study. Additionally, with only one exception, no current textbooks on reproductive physiology have been found that comment on any temperature phenomenon related to parturition.
Detection of parturition in animals has been accomplished in various ways. For example, U.S. Pat. No. 4,707,685 (Carrier et al.) discloses a system for detection of parturition which in effect is a continuity circuit. When a cow enters parturition, a thin wire, disposed about the animal's vulva, is broken and thus continuity in an electric circuit is interfered This lack of continuity sets off an alarm. U.S. Pat. No. 4,936,316 (Jewett) discloses the monitoring of the swelling of the animal's vulva.
Body pressure sensors have been utilized in conjunction with gathering information during parturition For example, U.S. Pat. No. 3,989,034 (Hojaiban) discloses an apparatus for determining the heart rate of a fetus during labor. The device comprises a means for receiving a measured fetal heart rate signal; a means for receiving a uterus pressure signal; and a means for determining an actual fetal heart rate based upon the uterine pressure and the measured fetal heart rate.
As may be seen, there are apparatus for detection of the onset of parturition, but these devices have various drawbacks. The accuracy in determining the duration of contractions in the above described devices is very limited, and thus the warning time available to medical professionals is limited to a short period before the onset of parturition.
Other types of sensors include blood flow monitors and heart contraction monitors. U.S. Pat. No. 4,915,113 (Holman) discloses a blood flow monitor comprising a plurality of transducers, an enclosure device, and an external monitor which is coupled to the enclosure by radio-telemetry. U.S. Pat. No. 4,993,427 (Barr et al.) discloses a heart contraction monitor comprising two ultrasonic transducers which are attached to an external monitor by a transmission line.
Other non-instrument based techniques for assessment of labor include symptomatic self monitoring, mammary stimulation, cervical distensibility indexing, and monitoring of fetal breathing movements. Each of these techniques has its advantages and drawbacks. But none of these techniques provides an accurate picture of the onset of parturition or of pre-term labor.
Another major concern in the birthing process is to determine the occurrence of fetal stress syndrome, which may occur before or during parturition. When fetal stress syndrome occurs, the fetus' temperature begins to climb dramatically, and the mother's temperature similarly undergoes a marked temperature increase. In order to reduce the risk of fetal mortality or injury, it is important to administer suitable treatment to remedy the problem as soon as possible. While the prior art has appreciated the importance of suitably administering treatment to the mother and fetus upon the occurrence of fetal stress syndrome, as seen in Weisz, "The Temperature Phenomenon Before Parturition and Its Clinical Importance," J.A.V.M.A. 102:123 (1943), the prior art has failed to adequately provide a means for detecting the onset of fetal stress syndrome and automatically administering the required treatment.
The automatic administration of drugs based upon medical characteristics of the patent are utilized in areas such as high blood pressure treatment, blood oxygen concentration problems, and the treatment of diabetes. For example, U.S. Pat. No. 4,003,379 (Ellinwood) discloses a medication dispenser which is inserted into the body and will dispense upon particular conditions being present. The dispenser comprises at least one sensor, control circuitry, a power source, a dispensing means, and medication storage means. Sensors and logic control circuitry are provided within the dispenser for measuring the existence or absence of a particular condition such as high blood pressure.
U.S. Pat. No. 4,543,955 (Schroeppel) discloses a medical implant which includes a sensor assembly disposed remotely from the implant, signal converting circuitry for converting the signals from the sensor to a coded signal, a transmitting means for transmitting the coded signal, and an activation device for receiving the coded signal and actuating the activation device based upon the coded signal. The parameters sensed by this system are body temperature, blood oxygen concentrations or blood potassium concentrations. Additionally, the activation device may be a drug infusion device.
U.S. Pat. No. 4,596,575 (Rosenberg et al.) discloses an insulin dispenser. The device comprises an implant having a transducer, an electronic control unit, a piezoelectric pump and an insulin reservoir. In operation, an external controller provides an actuation signal to the transducer which in turn sends an actuation signal to the electronic control unit. The control unit actuates the piezoelectric pump which in turn forces insulin to be dispensed from the reservoir.
Although current technology is available for comparing measurements expressed in quantitative form with quantitative tolerance limits and automatically delivering a dose of medication when those limits are exceeded, the evaluation of uterine contractions and the administration of labor inducing or retarding drugs has until now often been a qualitative one beyond the capabilities of the known state of the art identified above.